A new study on wheat shows that rise of atmospheric carbon dioxide will prevent plants from using nitrates to make proteins.

The study, conducted by researchers at the University of California, Davis, found that plants exposed to higher levels of carbon dioxide tend to reduce assimilation of nitrate into proteins leading to poor-quality grains.

According to Environment Protection Agency, a rise in temperature and carbon dioxide concentration can increase crop yield temporarily in some areas. However, further increase in warming will cut crop yields.

A new report by United Nations said that yields of major crops such as wheat and barley will start decreasing by 2030. The agency also said that demand for food is expected to rise by about a rate  of two percent a year.

The present study shows that quality of wheat, which is the staple food in several countries, is already on the decline.

"Food quality is declining under the rising levels of atmospheric carbon dioxide that we are experiencing," said lead author Arnold Bloom, a professor in the Department of Plant Sciences, according to a news release. "Several explanations for this decline have been put forward, but this is the first study to demonstrate that elevated carbon dioxide inhibits the conversion of nitrate into protein in a field-grown crop."

Note that the study at UC Davis was conducted on field crops and not on plants grown in a lab.

The samples of wheat used in the study came from a previous test conducted in 1996 and 1997 in the Maricopa Agricultural Center near Phoenix, Ariz. During the experiment, researchers pumped different concentration of carbon dioxide in test plots.

Leaves from the plants were then frozen, dried and stored. Researchers at UC Davis now employed new methods of nitrate estimation to check crop quality.

According to Bloom, the current study supports the findings from other researches that show that protein levels in common plants decline by eight percent under high CO2 levels.

"When this decline is factored into the respective portion of dietary protein that humans derive from these various crops, it becomes clear that the overall amount of protein available for human consumption may drop by about 3 percent as atmospheric carbon dioxide reaches the levels anticipated to occur during the next few decades," Bloom said in a news release.

Of course, the nitrogen uptake by plants can be increased using nitrogen-based fertilizers. But, these chemicals can destroy the crop land and leach into water bodies.

The study is published in the journal Nature Climate Change.

Related research has shown that climate change could lead to increase in diseases in wheat plants.